A mood disorder, bipolar disorder causes extreme mood swings - from the lows of depression to the extreme highs of mania. It's caused by a chemical imbalance in the brain and tends to run in families, though it is sometimes triggered by psychological stress.

Zeta-Jones, 41, sought treatment after her life hit a rough patch, her representative told People magazine. Zeta-Jones' husband, Michael Douglas, was diagnosed with stage 4 throat cancer last year.

Bipolar disorder can be devastating, disrupting lives and sometimes leading to suicide. But the good news for Zeta-Jones and fellow bipolar sufferers is that the illness can often be managed with medication - typically a mood-stabilizer - and psychotherapy.

In addition, certain lifestyle strategies often prove helpful, according to the American Academy of Family Physicians. These include keeping a regular daily routine, taking steps to minimize psychological stress, avoiding caffeine, and joining a support group.